BIND 10 #2092: RBNode parent pointer updates

[BIND 10 Development]

#2092: RBNode parent pointer updates
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |                       Status:  new
            Priority:  medium        |                    Milestone:  Next-
           Component:  data source   |  Sprint-Proposed
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |  scalable inmemory
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 - Make sure the parent of a root node (of some subtree) points to the
   upper level node (it's currently NULL; the root node should be
   distinguishable by the newly introduced "ROOT" flag)
 - Introduce a new method "getUpLevelNode" (or rename it as
   appropriate).  It takes a node and returns the parent of the rot
   of its subtree (i.e, it returns the node's immediate ancestor in
   the domain hierarchy).  If the node is at the top level (which
   should be absolute), it will return the null node
 - at this point, we should probably consider replacing the sentinel
   NULL node with a NULL pointer.  In my experiment I found it could
   be quite confusing if we have both the concept of "root" and
   "NULL node"

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Ticket URL: <http://bind10.isc.org/ticket/2092>
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